1. Field of the Invention
The present invention relates to an ink jet head applied, for example, to a printer, a facsimile, or the like, and also relates to an ink jet recording apparatus equipped with the ink let head.
2. Description of the Related Art
There is known a conventional ink jet recording apparatus that records characters and images on a recording medium by using an ink jet head having a plurality of nozzles for discharging ink. In this ink jet recording apparatus, the nozzles of the ink jet head are formed in a head holder in such a position as to face the recording medium. The head holder is mounted on a carriage and performs scanning in a direction perpendicular to a transport direction of the recording medium.
FIG. 11 is an exploded schematic diagram showing an example of such an ink jet head. As shown in FIG. 11, a plurality of grooves 112 are formed in parallel in a piezo-electric ceramic plate 111, and the grooves 112 are separated by side walls 113. One end portion of each groove 112 in the longitudinal direction extends up to one end face of the piezo-electric ceramic plate 111, whereas the other end portion of each groove 112 does not extend up to the other end face of the piezo-electric ceramic plate 111 and gradually decreases in depth. Electrodes 114 for applying drive voltages are formed in the opening-side surfaces of both side walls 113 of each groove 112 so as to extend in the longitudinal direction thereof.
An ink chamber plate 116, which defines a common ink chamber 115 communicating with the end portion of each groove 112 where the depth is decreased, is joined to the piezo-electric ceramic plate 111 on the side where the grooves 112 are opened.
A flow path substrate 118, which seals one side of the common ink chamber 115 and has a communicating hole 117 being in communication with an ink flow path for supplying ink to the common ink chamber 115, is fixed onto the ink chamber plate 116.
An ink reservoir 119, which constitutes a portion of an ink flow path for supplying ink into the common ink chamber 115 via the communicating hole 117, is formed in this type of flow path substrate. A finely meshed filter 120 made of stainless steel (SUS), for example, is formed within the ink reservoir 119.
A nozzle plate 121 is joined to the end face of the joined body of the piezo-electric ceramic plate 111 and the ink chamber plate 116 on the side where the grooves 112 are opened. Nozzle apertures 122 are formed in the nozzle plate 121 in such positions as to face the respective grooves 112 of the nozzle plate 121.
In the ink jet head constructed in the above-mentioned manner, when the ink is supplied to the grooves 112 via the communicating hole 117 and predetermined driving electric fields are applied to both side walls 113 of a predetermined groove 112 through the electrodes 114, the side walls 113 are deformed to change the capacity of the predetermined groove 112 so that the ink can be discharged from the groove 112 through the nozzle aperture 122.
Further, with an ink jet recording apparatus on which an ink jet head having this type of structure is mounted, for example, it is necessary to implement a filling operation for supplying ink from an ink reservoir at start-up, before printing, and the like, at a predetermined timing, to fill the inside of the grooves with fresh ink, or a filling operation for preventing clogging of nozzle apertures 122 by discharging ink from the inside of the grooves, known as a cleaning operation.
These types of ink filling operations are performed, for example, by sealing an end of a head tip of the ink jet head by using a cap or the like, and absorbing the inside of the grooves 112 from the nozzle apertures 122 with an absorbing apparatus such as a pump. The ink from the ink reservoir is thus filled within the respective grooves 112. The ink within the grooves 112 is then discharged from the nozzle apertures 122. With this type of ink filling operation, air bubbles in internal spaces of the head, for example, the ink reservoir 119, the common ink chamber 115, or inside each of the grooves 112, are also discharged from the nozzle apertures 122 along with the ink.
However, with a conventional ink jet head, there are relatively large volumetric changes in the ink that passes through the ink reservoir, which is a space around the filter, and this invites a reduction in the ink flow rate within the ink reservoir during the aforementioned ink filling operation, for instance.
If the ink flow rate decreases within this kind of ink reservoir, then air bubbles generated in the internal spaces of the head, that is in the ink reservoir, the common ink chamber, or the inside of each of the grooves cannot be efficiently discharged from the nozzle apertures during the ink filling operation, and therefore the air bubbles remain in the internal spaces of the head after the ink filling operation.
The air bubbles thus remaining in the internal spaces of the head become causes that exert a harmful influence on a head vibration system. For example, for cases in which the air bubbles remain within the grooves, the internal pressure of the grooves during the ink discharge operation will be absorbed by the air bubbles, and therefore there is a problem in that a predetermined pressure is not applied to the ink within each of the grooves, and the ink discharge characteristics are thus reduced. On the other hand, for cases in which there are air bubbles remaining in ink flow paths such as the common ink chamber, the ink reservoir, and the like, this becomes a problem in that it invites an insufficient supply of ink to each of the grooves, and as a result, the ink discharge characteristics are thus reduced.
Further, the location at which these types of air bubbles are generated differs depending upon the ink filling operation, and therefore dispersion in the ink discharge characteristics develops, ink supply insufficiencies develop, and each problem develops irregularly. The ink discharge characteristics are consequently reduced, and lastly this invites a reduction in printing quality.
In addition, if ink discharge is performed in the state in which air bubbles remain in the internal spaces of the head, then there is also a problem, for example, in that the air bubbles are discharged form the nozzle apertures along with the ink, and this invites printing failure.
There is also a problem in that each of the aforementioned problems becomes markedly worse for cases of using water based ink having poor air bubble permeability with respect to the ink, and for cases of using large sized ink jet heads with which the amount of ink discharged within a unit time is large.